Among contaminating metals to be caught into a silicon substrate during oxidation and diffusion processes of the silicon substrate, Cu has an extremely high diffusion velocity and easily diffuses into the silicon substrate. The diffused Cu deteriorates the device properties, such as electric properties. It is thus important to control the thermal process so as to decrease the amount of Cu that diffuses into the silicon substrate.
To measure the concentration of Cu within such a substrate, an analysis method is primarily used by utilizing an atomic absorption spectrochemical (hereinafter called “AAS”) method or a secondary ion mass spectrometric (SIMS) method. Particularly, the AAS method is capable of high sensitive analysis. However, the method utilizing the AAS method is obliged to analyze a silicon substrate by fully dissolving it in a mixed solution of hydrofluoric acid (hereinafter called “HF”) and nitric acid. As such, these methods were accompanied by the following problems. Namely, it was troublesome to conduct the measurement, and further contamination might be caused during pretreatment before the measurement of the Cu in the substrate. Moreover, substrates were destroyed in either method, thereby making it impossible to use the substrates again.
Thus, the present invention proposes a method for detecting the concentration of Cu within a semiconductor substrate without destroying the semiconductor substrate (see JP-A-9-64133 (64133/1997), for example). This method is used to heat a silicon substrate at a temperature of 600° C. or lower to diffuse Cu existent within the silicon substrate and collect the Cu toward obverse and converse surfaces of the silicon substrate, and analyze the obverse and converse surfaces by a method such as the AAS method or a total reflection X-ray fluorescence analysis (hereinafter called “TXRF”) method. According to this method and in case of a silicon substrate of P-type, a sufficient diffusion of Cu by heating the silicon substrate at 500° C. for 15 minutes in the atmosphere can be achieved.
Meanwhile, cleaning techniques inclusive of cleaning of a silicon substrate have been recently improved so that the concentrations of metals contaminating a silicon substrate have been lowered to about 1011 atoms/cm2.
However, the P-type silicon substrate used in the method of the JP-A-9-64133 has contained boron only at a concentration of about 1015 atoms/cm3, and has not been a silicon substrate doped with boron at a higher concentration. Thus, when Cu is existent within a silicon substrate at a lower concentration of less than 1011 atoms/cm2 in the case of silicon substrates internally doped with boron at higher concentrations such as P+ silicon substrates and P++ silicon substrates containing boron at concentrations of 3×1018 atoms/cm3 or higher, the Cu existent within the substrate causes an electrostatic effect with the boron so that the Cu is not sufficiently diffused toward the obverse and converse surface sides of the substrate, thereby problematically deteriorating an analysis precision in estimating a concentration of Cu contained within the substrate.